I have a handful of carts that work with no issues and I used the same commands to create this new cart, but it triggers an error with yum and I noticed the directory is missing files:
stack add appliance centos-sdc longname="centos-sdc" node=backend public=yes
stack set attr appliance centos-sdc attr=managed value=True
stack add cart centos-sdc
vi /export/stack/carts/centos-sdc/nodes/cart-centos-sdc-backend.xml
#Change this line:
<stack:script stack:stage="install-post">
#To this:
<stack:script stack:cond="appliance == 'centos-sdc'" stack:stage="install-post">
stack enable cart centos-sdc